In a typical steam injection well, steam is injected through a relatively small diameter uninsulated tubing string. This steam injection tubing string is run inside the well casing and forms an annular chamber therewith. Near the bottom of the steam injection tubing string is a thermal packer that seals the space between the tubing string and the well casing. This seal insures that steam is injected into the producing formation. The annular chamber is vented to the air to relieve any pressure build-up from steam leakage passed the packer or from any other sources of leakage.
Heat losses from steam injection wells result in significant added fuel costs. Typical heat losses from steam injection tubing are 400 to 600 BTU/hr. per foot of tubing. Commercially available insulated tubing can be used to reduce the heat losses to approximately 75 to 150 BTU/hr. per foot of tubing, however, insulated tubing is relatively expensive.
Filling the annular chamber with insulation can provide insulating value near that of commercially available insulated tubings, but a major cost reduction. To be effective, insulation must be kept dry. When insulation becomes wet, it loses much of its value as an insulator and may also lose its structural integrity. It is extremely difficult to maintain a dry state within a steam injection well because of steam leakage passed the thermal packer; condensation of the steam on surfaces kept cool by insulation wets the insulation. Also, ground water penetration into the well casing can and often does, occur. There is need, therefore, for a practical and efficient method for maintaining the structural integrity and insulating value of insulation used in a steam injection well.